1. Field of the Invention
The present invention relates to an image screen having characteristics of high contrast effect and adjusting emitted viewing angle region shape.
2. Description of Related Art
Recently, projector is widely applied in meeting, education, entertainment, and other aspects. Performance of a screen plays an important role in image quality. Because of brightness and contrast, usually it is necessary to lower environment brightness around the screen to view clear and colorful image.
For conventional screen, for example US Patent Publication No. U.S. 2006/0103929, a stack layer composed of a plurality of dielectric layers is provided. The layers with high indexes of refraction and the layers with low indexes of refraction are alternately stacked, such that a portion of light with specific wavelength is reflected. FIG. 1 shows a conventional image screen. Referring to FIG. 1, a screen 10 has a transparent substrate 11. An optical film layer 12 is disposed on two surfaces of the transparent substrate 11. The optical film layer 12 is composed by a plurality of dielectric layers with high index of refraction 12H and a plurality of dielectric layers with low index of refraction 12L which are alternately stacked. The optical film layer 12 reflects light with some wavelength.
Further, a light absorbing layer 14 is disposed on an edge to receive the non-reflected portion of the light, and a light diffusion layer 13 is disposed on the other edge. Image light generated by a display is projected from the light diffusion layer 13 to the screen 10. The optical film layer 12 reflects light with a portion of wavelength. Finally, remaining light is absorbed by the light absorbing layer 14.
In the conventional screen, a same asymmetric film layer 12 is respectively plated on two sides of the substrate 11, and the film layer 12 of each edge reflects wavelengths of red, green, and blue lights, but with a low reflectivity. The same asymmetric stack layer film on two edges can enhance the reflectivity. Materials of high and low (H, L) indices of refraction are dielectric material with large thickness, so a problem of poor adhesive property exists, and the film layer 12 easily breaks, such that it is impossible to be applied to a flexible substrate.
People in the industry still continuously researches and develops other designs of the image screen, so as to improve the performance.